The US Core specification doesn't provide guidance for implementers about how narrative should be populated or what should appear in it.  Narrative is an essential fallback for exchanged content when systems might not understand all discrete data and is also the primary source for displayed content when it is included in documents.  Narrative is best provided by the 'source of truth' system as it best understand what content is most important for human understanding of the instance.  Da Vinci IGs such as PCDE are dependent on narrative being present.  While we could supplement all US core resources with guidance about narrative population, it would be better for this guidance to originate in US Core and thus be consistent across all uses of the resources.